The present invention relates to a multiple disk clutch in a frictional engagement structure using multiple disks, and more particularly, to a cushioning disk spring and spring bearing member arranged between a clutch plate and a piston.
With a multiple disk clutch in the related-art frictional engagement structure using multiple disks, driven plates and drive plates are splined to respective drums that produce relative rotation. When pressed by a piston, the driven plates and drive plates are frictionally engaged with each other to cause unitary rotation of the two drums. With such a frictional engagement structure, a cushioning disk spring is arranged between the piston and the drive plates so as to prevent abrupt change in the engagement force of the driven plates and drive plates, achieving smooth engagement of the clutch. In this connection, refer to Japanese document P2002-213581A.
With the above multiple disk clutch, however, the disk spring is typically formed of steel that is a material harder than that of the drums. Thus, during non-engagement of the clutch, the free disk spring rotates with respect to the outer-periphery-side drum due to rotational variations, and makes slide contact with the inner peripheral wall of the drum, causing wear of the drum. Such wear can be prevented by hardening the drum through heat treatment, which causes, however, not only an increase in the number of working processes and in manufacturing cost, but also difficult achievement of sufficient strength even through execution of heat treatment, which is a case that the material is aluminum, for example. Alternatively, drum wear can be prevented by providing claws to the disk spring for its engagement and fixing to the drum. With this alternative, however, the claws make contact with splines of the drum to transfer thereto torque in the direction of rotation, leading to possibility of causing damage to the splines.